Telephone system



Sept. 1, 1942. H. HOVLAND 2,294,500

TELEPHONE SYSTEM Filed Oct. 16, 1940 10 Sheets-Sheet 1 'FIG. 4 FIG. 7

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sue 3 A TTORNEV Sept. 1, 1942. HOVLAND 2,294,560

TELEPHONE SYSTEM flii iiii a in 0, n

Filed Oct. 16, 1940 10 Sheets-Sheet 2 TONE INI /ENTOR H HUI/LAND ATTORNEV FIG. 2

MARGINAL Sept. *1, 1942. H. HOVLTAND I 5 0.

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INVENTOR H. Hal LAND 4 7 TORNE 1 Fer Sept; 1, .1942. I H. HOVLANDTELEPHONE SYSTEM Filed Oct. 16, 1940 10 sheets-sheet 4 IINI/ENITORHHOVLAND A T TORNEV Sept. 1, 1942. H. HOVLAND 2,294,500

TELEPHONE SYSTEM Filed Oct; 16, 1940 10 Sheets-Sheet 5 H a at F El 2 3 QQ m x 53; '0 0 w z INVENTOR H. HOVLAND A TTORNEV Patented Sept. 1, 1942UNITED ST TELEPHONE SYSTEM Application October 16, 1940, Serial No.361,365

(Cl. 179-l8) 16 Claims.

provement in the supervisory facilities of such systems.

It is usual in automatic telephone systems comprising-a main and abranch office to provide switching selector repeaters in the branchofiice forselecting a-' trunk to the main office, for re-* peating alldial impulses over the selected trunk to the main office on calls tosubscribers in the main office or other offices of the system, and forrepeatingdial impulses over the selected trunk to the main oflice oncalls to subscribers in the branch oflice until as many digits have beendialed as are needed to determine that the called subscriber is locatedin the branch office, the

trunk to the main office being released as soon as these digits havebeen dialed and the succeding trains of dial impulses being eliective'to complete the desired connection through switches in the branchoffice. Among the'patents disclosing branch omce systems and switchingselector repeaters are the patent to E. J acobsen No. 1,537,306,'May12,1925, and patents to H. Hovland No. 1,799,796, April '7, 1931, andNo. 2,025,389, December '24, 1935.

According to the invention, an improved switching selector repeater isprovided in a branch office of an automatic telephone system, theselector repeater having various new and novel features. One of thefeatures is a circuit arrangement whereby the selector switch of abranch office selector repeater absorbs the last digit of the branchoffice code if this digit is a particular numerical value, or one ofcertain numericalvalues, and immediately hunts for an idle trunk in thecorresponding level of its bank; but does not absorb the last digit ofthe branch ofice code, if the last digit is some other numerical value.This arrangement enables the connection of trunks to different orders oflocal switches in different levels of the bankof the selector of aselector repeater, thereby minimizing the numafterrelease of thesele'cted'trunk'to the main office on a call to a subscriber in :thebranch office.

Another feature is a branch oflice selector/repeater .arranged toautomatically release the selected trunk to the main office in case.nofdial impulses are received within a predeterminedinterval of time,such for instance as twenty-four seconds.

A further feature is-a branch ofiiceselector repeater arranged I torelease the line finder through which it is connected to a calling: linewithin a predetermined interval, for instance two minutes, after theselected trunk to the main oflice is released due to a permanentsignalcondition.

Another feature is a branch office-selector repeater arranged to operatea'line lock-outrelay on calls from lines equipped with such relays incase nodial impulses are receivedfrom the. calling line within apredetermined intervalyof. time, for instance two minutes.

Another feature is a branch officeselectorrepeater arranged to deny torestricted service-subscribers access to main office trunks and'aaccessto trunks in any desired level of the selector, .the restricted servicesubscribers lines being connected to one or more particular subgroups.in the banks of the line finders throughwhich the lines are connectedto selector repeaters.

Another feature is a branch office selector" repeater arranged to routecalls to the mainoffice through the non-numerical trunking switch and toroute calls toanother central o'ffice througha level of the numericalselector switch in response to the dialing of two digits.

Another feature is a branch omceselector repeater arranged to routecalls to an operatorin response to. the dialing of either an ltXicode oran Xll code, the letter X in each case representing a-digit of anynumerical value.

'I'hese'and other features of the-invention are embodied in thetelephone system represented schematically in the drawings which form apart of this specification; and a clear and. complete understanding ofthe invention-will be facilitated by considering the system and theselectorrepeater circuits'shown in the drawings. 'The invention'is,however, not limitedin itsapplication to the particular system shown butis generally applicableto any system comprising automatic main'andbranch-ofiices.

--Referring to the drawings,

Fig. 1 shows in a branch ofiice subscribers stations A and B, 'lines Liand L2, linecircuits switches when used as line finders. line finder,selector and connector switches LF,

LCI and LCZ, a line finder LF and a connector BCI;

Figs. 2 and 3 show a branch ofiice selector repeater SRI;

Figs. 4 and 5 show a branch office selector re- 5 Fig. 6 shows permanentsignal timing apparatus TA and miscellaneous alarm and registerapparatus MA in the branch omce;

Fig. 7 shows an intermediate local selector BS3,

a service code selector SCS, connectors BC? and B03, and subscribersstations X and Y, all in the branch office;

Figs. 8, 9 and 10 show various trunking and numbering schemes which mayobtain in a main and branch ofiice system; and

Figs. 11 and 12 show the relative positions in which Figs. 1 to 7 are tobe placed to form operative arrangements.

eThe subscribers stations are of the type emcircuits LCI and L02 and theline-finder circuit .LF are similar to those disclosed in the patent toT. L. Dimond No. 2,210,068 granted Aug. 6, 1940. The line circuit LCIincludes a line relay M and a permanent signal lock-out relay I6. Theline circuit LCZ is similar to the line circuit LCi except that it isnot provided with a permanent signal lock-out relay.

The line-finder, selecter and connector switches are of the well-knowntwo-motion st-ep-by-stern. type. Reference may be had to pages 53 to 65,inclusive, of .the second edition of Automatic Telephony by Smith andCampbell for a description of the structure of such switches and theiroperation when used as selectors and connectors. Reference may be had tothe patent to '40 R. L. Stokeley, No. 1,799,654, granted April '7, 1931,and to the aforementioned patent to T. L. Dimond for .a description ofthe operation of such Each of the SCS, BCI, B02 and B03 i represented inFigs. 1 and 7 by a set of brushes and one, two, or three sets ofterminals, all magnets, relays and other associated apparatus beingomitted; except that.

the line finder ICE is further represented by three 3U sets of contactsprings 25, 26 and 28 and release .magnet 29. The numerical selectorswitches BS! and BS2 of the selector repeaters SRI and SR2 and thebranch office selector BS3 are shown in.

detail. The bank of each of selectors BSI and BS2 is represented by foursets of terminals.

The terminals H and 2' represent the first levels in the bank ofselectors BSI and BS2; terminals 12 and 2'12 represent levels connecteddirectly to connectors; terminal 13 represents a m level of the bank ofselector BSI connected to third selectors BS3; terminals 213 represent alevel of the bank of selector BS2 connected to trunks to another Office;and terminals 14 and 2'! represent the tenth levels of the banks of U5selectors BS1 and BS2.

The selector repeater SRI shown in Figs. 2 and 3 includes a trunkhunting switch TSI comprising brushes 9!, 92 and S3 and a steppingmagnet 90, a numerical selector switch BSI. comping magnet 15, rotarystepping magnet 16 and release magnet 11. The selector repeater SR]further includes a line relay 41, impulse repeating relay 45, switchingrelay 40 and other control relays as hereinafter described. Two terminalstrips 18 and 19 are provided for interconnecting the segments ofcommutator 6'6 and the windings and contacts of control relays to 80,inclusive, 88 and 89 as required for any particular trunking arrangementand numbering scheme. There are sixteen terminals in each of theterminal strips 18 and 19, which terminals are referred to in thedetailed description as being numbered from 1 to 16, beginning at thebottom of each strip.

The system represented in Figs. 1, 2, 3, 6 and 7 conforms to thetrunking plan shown in Fig. 8. Referring to Fig. 8, the trunkingarrangement is designed to provide for a total of 9,700 fivedigitsubscribers numbers in a main office and a branch office. Numbers from80000 to 81999 and 84000 to 89999 are assigned to themain office;numbers from 82000 to 82999 and 83300 to 83999 are assigned to thebranch oifice; and it requires a maximum of two digits to determinewhether a called number is located in the branch or in the main ofiice.The first digit of the main and branch ofiice numbers could be anydesired digit other than 0 to 1. The digit 0 is used for calling anoperator and the digit 1 is employed for special service codescomprising three digits, the first two of which are the digits 11.

In the branch office, the subscribers lines terminate in line-finderswitches, such as LF, and in the banks of connector switches, such asBC. The line finders are used to establish connections with lines whencalling, and the connectors with lines when called. The station Arepresents a calling station and the stations X and Y represent calledstations. Each line finder is permanently associated with a selectorrepeater SR which includes a numerical selector switch BS and anon-numerical trunk hunting switch TS. The terminals in the banks of thetrunk hunting switches connect to trunks such as TI leading to the mainoflice and terminating in incoming selectors such as ISI. The terminalsof the first level of the bank of the selector switches BS of theselector repeaters SR are connected to service code selectors. Theterminals of the second level are connected to third selectors such asBS3; the terminals of the third to ninth levels are connected toconnector switches; and the terminals of the tenth or zero level of thebank are connected to trunks leading to an operators position.

In the main ofiice, the subscribers lines are in like manner terminatedin the banks of linefinder switches (none being shown) and in the banksof connectors such as C. The station Z represents a subscribers stationto which the connector C has access. In addition to the incoming firstselectors such as ISI for extending calls originated by subscribers inthe branch office, local first selectors (not shown) are provided foruse in extending calls originated by subscribers in the main office. Thefirst selectors, both incoming and local, have access to the same orsimilar groups of trunks. Terminals of the first levels of the incomingselectors such as ISI are connected to auxiliary first selectors forabsorbing a preliminary impulse. The terminals of levels 2 to "I,inclusive, and level, 9 may be connected to trunks leading to otherofiices. The terminals in level 8 are connected to second selectors suchas S2 and the terminals -and fifth digits being 'the dialing of thein-the-tenth or zerolevelof the incoming first selectors are not used.The terminals in the secondland third levels of the second selectors S2are connected totrunks leading to incoming selectors the branch officefor use-in completing calls from .main oilice subscribers to sub--seribers in the branch 'o'ffice. the'otherlevels of the secondselectors arecon- -nected to third selectors such as S3. ,The terininalsof alllevels of the third selectors S3 are -connected -to connectorswitches C having The terminals in access to subscribers lines.

:When the line-finder switch LF associated with the selector repeaterSRI of Figs. 2 and 3 starts to hunt for acalling line, the trunkhuntiing s'witchTSi starts to hunt foran idle trunk =to the main ofiice.When the calling subscriber dialsa first digit, the dial impulses arerepeated overthe trunk to the main office and the brushes of selectorBSIare advancedto a corresponding level. If all. ofthe trunks to the mainoflice are busy, the selector BSI responds to the first digit and if thecalledstation is in the branch office the call will be completed; but ifthe called station is not. in the branch ofilce, a busy tone istransmitted to the calling station. If the first digit is .0, theselector BSI hunts in the tenth level for .an idle trunk to an operator;and the trunk to the main ofiice is released. If the first *digit is l,the brushes of selector BS5 are stepped up to the first level and arethen restored to nor- -mal; if the next digit is any other than 1, the

operation is the same as if no preliminary digit had been'received; butif the second digit is also the digit 1, the brushes are again steppedup to' the first level and rotated therein to select an idle servicecode selector SCS. If the first digit dialed is any other than'O, l or8, the brushes of selector 'BSl are advanced to the corresponding level,and remain in this position without trunk hunting while succeedingtrains of dial impulses are'repeated over the trunk to the. main officeto control the completion of the desired connection. If the first digitdialed is 8,'the called station is either in the branch or in the mainofiice; and the brushes are advanced to level 8, and are then restoredto normal. When the second digit is dialed, the impulses are repeatedover the trunk to the main oifice and the brushes are again advanced tothe corresponding level. If the second digit is any other than 2 or 3,the called station is in the main office, the brushes of selector BSIare held opposite the selected level without trunk hunting, andsucceeding trains of dial impulses are repeated over the trunk' to themain omce to control the selector and connector switches through whichconnection with the called station in the main ofiice is completed, Ifthe second digit is the digit 2, the trunk to the main oflice isreleased and the brushes are advanced in the second level to select anidle selector BS3, the impulses created by the dialing of the third,fourth transmitted through the brushes of selector ES! to control theoperation of the selector B53 and a connector B03 to complete connectionwith the called station. If the second digit is the digit 3, the brushesof selector BSI are again returned to normal and the trunk to the mainorfice is released. When the third digit is dialed the brushes ofselector BSI are advanced to the corresponding one of levels 3, 4, 5,-I5, I,-=8 or 9 and advanced in this level to select an'idle connectorB02, the impulses created by fourth andfifth digits being repeated:through the brushes of-selector BSI to tion is a restricted: servicestation, the actuation ofiithe springsx25 :of. the line finder so.indicates;

and, if thefirst digit'dialed is any other than 0, lior 8, the brushes"of selectorBSI are advanced in the corresponding level to. the 11throtary position and a busy toneis transmitted to the calling station. Insome trunking arrangements in which the selector repeater. SRI may beused, trunks to another omcemay :be connected to' a level of theselector BS5 and, when a restricted service subscriber calls this otherofiice, the operation of normalpost springs '19 efiectsthe advance ofthe brushes to the 11th rotary position to effect the transmission of. abusy signal to the calling station.

When the selector repeater SRI is connected to acalling station, itstarts the operation ofa common permanent signaltiming apparatus TA, Ifall of the subscribers lines are arranged for permanentsignal lock-out,and if no dial impulses are received within twenty-four seconds, theline finder is released, the trunk to the main ofiice is released, andthe permanent signal lock-out relay in the calling subscribers linecircuit is operated to .-'prevent connection of the line to anotherselector repeater. If some but not all subscribers lines are arrangedfor permanent signal lock-out,

the trunk to the main ofiice is released if no dial impulses arereceived within twenty-four seconds after connection of a calling lineto the selector repeater; and, after a-further interval of two minutes,the line finder is released and the permanent signal lock-out relay ofthe calling line .is operated in case the call is from a line includingsuch a relay. If the calling line does not include a lock-out relay,-theline will again be connected-t0 .a selector repeater. If none of thelines is arranged for permanent signal lock-out, and if no dial impulsesare received within twenty-four seconds after a calling line isconnected to the selector repeater, the trunk to the main oifice isreleased; but the selector repeater SRI is held until a furtherpredetermined interval has elapsed; whereupon a permanent signal alarmis operated as hereinafter described in connection with apermanent'signal condition existing on a line connected to selectorrepeater The timing apparatus TA comprises means for measuringintervalsof from two to four minutes, means for measuring intervals of fromtwenty to thirty minutes, means for measuring intervals ofapproximatelytwenty-four seconds,

andmeans for releasing selector repeaters to which are connected lineson which permanent calling conditions exist.

The means for measuring intervals of two to four minutes comprisesrelays I2I, I22 and I23. When these relays are not in use, ground isconnected through back contacts of relays I2I and I23 to conductor I25.When ground is connected to start conductor I28, relay I2I operates,disconnecting ground from conductor I25. The operation of relay I2Icauses the operation of relay I22, from two to four minutes later. Theoperation. of relay I22-causes-the operation of relay I23. Theoperationof relay I23 causes the release of-relay -I2I'and connects ground toconductor I24. The release of relay I2I causes the release of relay I22;the release of relay I22 causes the release of relay I23; and therelease of relay I23 disconnects ground from conductor I24, connectsground to conductor I25, and connects relay I2I to the start conductorI20. This cycle of operations is repeated as long as ground is connectedto start conductor I20. Relay I2I is slow in operating to insure theconnection of ground to conductor I25 for a required interval of time,and relay I23 is slow in releasing to insure the disconnection of groundfrom conductor I24 for a required interval of time.

The means for measuring intervals of twenty to thirty minutes comprisesrelays II, I52 and I53 which, upon connection to ground to startconductor I50, operate to connect ground to conductor I55 for a shortinterval once every twenty to thirty minutes and to disconnect groundfrom conductor I54 for a short interval once every twenty to thirtyminutes.

The means for measuring intervals of approximately twenty-four secondscomprises timing relays I3I, I32 and I33 and a start relay I34. Uponconnection of ground to start conductor I30, relay I34 operates closinga circuit for operating relay I3I. Relay I3I closes a circuit foroperating relay I35 to disconnect battery from conductor I03 and othersimilar conductors. Relay I3I also closes the circuit for operatingrelay I32; and, twenty-four to twenty-eight seconds later,

relay I32 operates. Relay I32 closes a circuit for operating relay I33.Relay I33 closes a holding circuit for relay I35, causes the release ofrelay I34, and connects ground to conductor I05. The release of relayI34 causes the successive release of relays I3I, I32, I33 and I35. Therelease of relay I33 reconnects start relay I34 to conductor I30; andthe above-described cycle of operations is repeated as long as ground isconnected to conductor I30. By the connection of ground to conductorI05, the release of main ofiice trunks is effected in selector repeatersconnected to lines on which a permanent signal condition exists.

The means for releasing selector repeaters connected to lines in a,permanent calling condition comprises relays I42 to I45, inclusive, theoperation of which is hereinafter described in detail.

Referring now to the detailed circuits disclosed in Figs. 1, 2, 3, 6 and7 arranged according to Fig. 11, assume that a call is originated atstation A. Upon removal of the receiver by the calling subscriber, acircuit is closed for operating the line relay I4 of line circuit LCI.This circuit is traced from battery through the middle and upperwindings of relay I4, inner upper back contact of relay I4, conductor I2of line LI, through the telephone instrument at station A, conductor IIof line LI, inner lower back contact and lower winding of relay I4 toground. Relay I4 is thereby energized sufiiciently to close its outerfront contacts without afiecting its remaining contacts. At its upperfront contact, relay I4 closes a circuit including the inner lower backcontact of relay I6, the outer upper back contact of relay I4, andconductor I5 for operating the start relay I8, relay I8 being thereuponeffective to start the operation of an idle line finder LE to search forthe calling line as described in detail in the aforementioned patent toT. L. Dimond. At its outer lower front contact, relay I4 closes aconnection from its middle winding, through back contacts of relay I5and conductor I3, to the test terminals of the sets of terminals in thebanks of the line-finder switches having access to the line LI. As soonas a line finder LF starts searching for the calling line, groundpotential is connected to conductor 33, thence through the upper backcontact of relay 85, a, lower back contact of relay 51 and the outerback contact of relay 50 to the winding of relay 55, thereby operatingrelay 55 of the selector repeater SRI to start the trunk huntingoperation of switch TSI as hereinafter described. When the brushes ofthe line finder LF connect with the terminals 2| to which the callingline is connected, ground potential is connected through the lower brushto conductor I3 to fully energize the middle winding of relay I4, and acircuit is closed for operating the line relay 4'! of the associatedselector repeater SRI. The energization of the middle winding of relayI4 upon connection of ground potential to conductor I3 completelyoperates relay I 4, thereby disconnecting the line conductors II and I2from the windings of relay I 4 and disconnecting ground potential fromconductor I5 so as to release start relay 48 if there is at this time noother calling line in this same line finder group awaiting extension toa selector repeater. The circuit for i operating the line relay 4'! istraced from battery through the lower winding of relay 41, the upperback contact of relay 44, a lower back contact of relay 43, conductor32, the middle brush of line finder LF, conductor I2, through station A,conductor II, upper brush of line finder LF, conductor 3|, an upper backcontact of relay 40, inner lower back contact of relay 44, upper windingof relay 4?, upper back contact of the 11th rotary step springs 58,inner lower back contact 5 of relay 43, inner lower back contact ofrelay 57,

through the primary winding of the dial tone transformer 53 to ground.Relay 47 closes circuits traced from ground through a lower back contactof relay 40 and the lower front contact of relay 4? for operating relays42 and 53, the circuit for operating relay 53 further including thelower back contact of release magnet 11 and the back contact of thevertical off-normal springs 57. At its outer upper front contact, relay42 connects ground to conductor 33 to hold the line finder LF' and relayI4 in usual manner, and to maintain the operation of relay 55 in casethe switch TS! has not completed its trunk hunting operation. Relay 42also closes a circuit for operating the start relay 39 of the ringingand tone supply apparatus RA.

The aforementioned operation of relay 55 connects the winding andinterrupter contact of stepping magnet 93 of trunk hunting switch TSI,through the outer upper front contact of relay 55, inner back contact ofrelay 59, and .through the test brush 93 of switch PS5, to the testconductor of the trunk connected to the terminals with which the brushesof switch TSI are then in engagement. Relay 55 also closes a circuitfrom ground through its outer lower front contact and the winding ofrelay 55, in series with the interrupter contact and winding of steppingmagnet 33. If the trunk connected to the terminals then engaged by thebrushes of switch TSI is busy, the test conductor is connected to groundthereby preventing the operation of relay 50 and operating magnet 93.Magnet opens its own operating circuit, and its release advances thebrushes of switch TSI to the next set of terminals. The operation andrelease of magnet 90 is repeated to advance the brushes step by stepuntil an unguarded set of brushes is encountered. If the trunk,connected to the terminals with which the brushes of switch TSI is inengagement when relay 55 operates, is idle, orassoon,

thereafter as the brushes are advanced. into engagement with a set ofterminals, connected to an idle trunk, relay 50is operatively'energizedin" series withthe stepping magnet 96.]. Since'the stepping magnet 9|]is marginal, it, does not operate inseries withrelay-Efl; and,therefore, no further advance of the. brushes". occurs.

ground at a front contact of relay 42.. With ,both' of relays 50 and41operated,a-circuitiszclosed for operating relay 455 main ofiic'e isconnected through-brushfll, the

upper front contact ofv relay. 45,.theouterrlower front contact of relay53; through" resistor 5.4, to battery; and the lower: conductor. ofitheselected trunk'T is connectedfthrough:brush.92.,'the

inner upper front contact of relay 56,, the lower front/contact ofrelay45, the outer upperfront contact f relay 53, through resistor 5 ltoground. The connection of battery and ground to the conductors of theselected trunk'Tto the main office effects the operation of thelinerelay (not shown) of the incoming selector associated with the trunkT in the main-office to preparethe incoming selector'for response todial impulses.-

Dial tone is transmitted'through the; windings of transformer 5B,and theupper winding of relay 41, to thecalling stationtoindicatethatthegsubscriber may start dialing. When the. subscriber dials thefirst digit of a called ,subscribers' number, relay 4'! is alternatelyreleased: and reoperated as many times as there are:units;in the digitdialed. The release of relay 4?, in-response to the first impulse,connects groundthroughits back contact, the outer lower front contact ofrelay 42, lower back contacts. of: relays:49 and43, to the winding ofrelay 5i and to :the winding of;

the vertical stepping magnet;.l'5.. Relay 5! operates, locks to theground on conductor. 33; disconnects its winding from the impulsecontact of relay 41, disconnectsv the dial tone transformer from the:upper winding ;.of :relay; 4?, and; connects ground potential directlyto this: winding. In case the calling, subscriber startsto dial before atrunk to the-main'office has been selected, thev operation of relay 5'!causes :the release of'relay 55, thereby stoppingthe operationroftrunk'hunting switchrTSl: The-operationof vertical stepping-magnet l5raises the brushes 6!, 62, 63 and 64 up to the first level oftheterminalbank; the

vertical-off-normal springs fil'being actuated'as' soon as the shaft ismoved out of itsnormal position. Withvertical off-normal springs 61actuated, the winding of therelay 53 is disconnected; from-the lowerfront contact of relay; 4! and is connected through'the middlefront'contact of' springs 6l and-a lower back contact ofrelay 44,

in parallel with the vertical stepping magnet 75 under the control ofthe lower back contact of relayAl. When relay 4'! reoperates at the endof the first impulse, magnet l5 releases; but relay53.is-a.slow-to-release relay and it -remains-operated until all of theimpulses in the train createdby-the dialing of the first digit have beenreceived. Relay 42.. is also slow in releasing and remains operatedduring the response-of relay;

Relay 50 connects ground-to test brush .93to. guard "the selectedtrunkto the main officeagainst seizurei With relay; 45 operated, theupper conductor of the selected: trunk T to the stepping magnet 15,thereby advancing the brushes GI, 62, Hand 64 to the level correspondingto the digit'dialed. Each releaseof relay41- further causes the releaseof :relay 45 to disconnect battery and ground from the conductors of thetrunk to the-main office and to thereby repeat the'dial impulses to theline relay of the incoming selector inthe main office. At-the.end-

of the train of impulses corresponding-tothe first digit, relay 4?remains operatedthereby causing a The release of relay-53- therelease ofrelay 53. disconnects battery and ground from theconductors of thetrunk:to the-main officeand closesa bridge across these conductors, thisbridge beingtraced from brush 9| through the uppercontact of relay 45,outerlower'back contact ofrelay 53; lower winding of relay 44, upperback contact-of relay 53, upper track contact of relay 48, innerupperfront contact of relay53, to brush-92 :of The lower winding ofrelay 44- is:

switch TSI. thereby energized in series with the linerelay of a secondselector in the main ofiice, the @current through the windingof relay 44being inthe nonoperating direction.

The normal post springs 69. areadjusted-tobe actuated on all levels; andthe actuation of these springs, as soon as the brushesare stepped up tothe first level of the bank, closesa circuit for operating relay 81.This circuit includessprings 69, the back contactlofxrotary;steppingmagnet 16; the upper back-contact of relay 49, the inner lower frontcontact of relay 53',- and theinner upper'back contact of relay 43;Relay 81' looks .through its lower front contact;.the middle upper backcontact of relay 43; the inner lower back contactof relay 45', conductor33, to groundat a:

front contact of relay 42. RelayBl preparesfor the operation of therotary stepping magnet [6 in case trunk hunting is requiredon the levelselected'inresponse tothe first train of impulses.

Assume first that the call is to an operator, .the first digit dialedbeing the digit 0. In this case, the brushes of selector BS!arepadvancedv to the tenth or new level; and, when-relay 53 releases, acircuit'is closed for operating relay 86. This circuit is traced fromthe winding of relay 86, through the lower back .contactof relay 8!, thetenth terminal of commutator 66, brush the lower back contact of relay86; upper back'contact of releasemagnet ll, inner lower backpcontact ofrelay 53,- to ground at the inner upper:

back contact of relay 43. Relay 83 closes a lock.-

ing'circuit through its inner upper front contact.

before its operating circuit'is opened at'its lower back contact, thelocking circuit includingback contacts of relays 43 and 40, conductor33, to.

ground at a front contact-of'relay 42. Relay 86 closes a circuit foroperating-the rotary stepping magnet'16'; through the Winding of magnet15, the outer lower front contact of relay 86-,- back contacts of relays83" and Min parallel, the upper front contact of relay 81, upper'backcontact of release magnet inner lower back contact of .re--

lay 53, to ground at a back contact of relay 43. The operation of magnet'56 steps the brushes 6|, 62, 63 and 64 into engagement with thefirstset of terminals in the tenth level and opens the locking circuitof relay 81. Relay ill releases, thereby causing the release of" magnet16; If

the trunk'connected to the first set of terminals:

Each release andreoperationof' relay 4'! inresponse'to-succeeding.impulses of the train created by the dialing ofthe This circuit is traced from battery is busy, the test brush 63encounters a ground potential which is extended through the lowermostback contact of relay 45, the middle lower back contact of relay 43,upper back contact of relay 49, back contact of rotary stepping magnet16, springs 69, to the winding of relay 81, thereby causing thereoperation of relay 81. Relay 81 again closes the circuit for operatingthe stepping magnet 16; and the brushes are advanced into engagementwith the next set of terminals. Relay B1 and magnet 16 are thuseffective to continue the advance of the brushes until a set ofterminals, connected to an idle trunk circuit OT, is encountered. If allthe terminals in the level test busy, the brushes are advanced to the11th rotary position in which contact springs 68 are actuated to connectthe busy tone source BT of appartus MA to the upper winding of relay 41,thereby transmitting an all-trunks-busy tone to the calling subscriber.If and when an idle set of terminals is encountered, there is no groundpotential connected to the terminal engaged by test brush 63 and relay49 is operated, the circuit for operating relay 49 is traced frombattery through the winding of relay 81, springs 69, back t,

contact of rotary stepping magnet 13, winding of relay 49, inner lowerfront contact of relay 86, lower back contact of the 11th rotary stepsprings 68, to ground at a front contact of relay 42. Re-

lay 81 is marginal and does not operate in series 3 with the winding ofrelay 49. The operation of relay 49 opens the short circuit aroundresistor 31, thereby connecting this resistor in series with the windingof the vertical stepping magnet 15, to prevent the further operation ofmagnet 15. Relay 49 closes a circuit from ground at the middle upperfront contact of relay 42, through the upper back contact of relay 83and the lower front contact of relay 43, for operatively energizing theupper winding of relay 43 in series with the winding of relay 4!. Theoperation of relay 4| may momentarily close a circuit for energizingrelay 43; but relay 43 is slow in operating and, as soon as relay 46operates, the circuit for energizing relay 43 is opened. Relay 4O locksthrough its lower winding to ground on conductor 33, disconnects thewindings of relay 41 from conductors 3| and 32, and connects conductors3|, 32, 33 and 34 through brushes 6!, 62, 63 and 64 to the selectedtrunk circuit OT. The operation of relay causes the release of relays41, 86, 42, 45, 49, 55, 56 and 4|. The calling line is thus connectedthrough conductors 3! and 32, brushes El and 52 and terminals 14, to thetrunk circuit OT which is effective in usual manner to connect a holdingground potential to the ter minal engaged by test brush 63, thencethrough brush 63 to conductor 33, to hold relays 43 and 51 of theselector repeater, to hold the line finder LF, and to hold the combinedline and cut-off relay [4 of the calling line. Reference may be had tothe patent of R. B. Buchanan et al., No. 2,233,282, granted Feb. 25,1941, for description of a trunk circuit associated with a trunk to anoperator. A class of calling subscriber indication is given in a circuitincluding the level contacts 26 of line finder LF', conductor 34, afront contact of relay 40, outer lower back contact of relay 83, brush64 and the terminal with which it is in engagement. One class of callingline is indicated by the connection of ground through a resistance 21 toconductor 34 as shown in Fig. 1; another class by the connection ofground directly to conductor 34; and a third class by the lack ofconnection of ground to conductor 34.

The release of relays 45 and 50 opens the loop across the conductors ofthe trunk to the main office, thereby efiecting the release of theassociated incoming selector in the main office. The main oifice trunkis not released until after the selector repeater has found an idletrunk to the operator or until the brushes have advanced to the 11throtary step position if all of the trunks are busy. Since the operatorstrunks are connected to the tenth level of the selectors of branch omceselector repeaters, the terminals in the tenth level of the incomingselectors associated in the main oifice with trunks from the branchoffice are not connected to operators trunks; but these incomingselectors trunk hunt in the tenth level and therefore the test terminalsin this level should be connected to ground to prevent the selection ofany of these terminals. Otherwise the incoming selector mightimmediately begin to release before the selector in the branch officehad found an idle trunk to the operator; and the line relay of theincoming selector might then be reoperated during release and therebyjamb the wipers.

When the call is released by the calling subscriber and by the operator,the holding ground potential is disconnected from the terminal engagedby test brush 63, thereby causing the release of relays 40 and 51 of theselector repeater SBA, and the release of the combined line and cut-offrelay E4. The release of relay 40 closes a circuit including backcontacts of relays 40, 41 and 42 for operating the release magnet 11 ofselector BS! and the release magnet 29 of line finlder LF. The brushesof the selector BSI and line finder LF are thereby restored to normal.When the shaft of selector BS1 reaches normal, the contact springs 61are restored to normal, causing the release of magnet 11; and when theshaft of line finder LF reaches normal, the contact springs 2-8 arerestored to normal, releasing magnet 29.

Assum next that the first digit dialed is a digit other than 0, 1 or 8,the called subscriber being located in some ofi'ice other than the mainor branch offices, and the call being completed over a trunk to the mainoffice. When relay 53 releases after the reoperation of relay 41 at theend of the last impulse in the train, it closes a circuit for operatingrelay 43. If the first digit is 4, 5, 6, '1 or 9, this circuit is tracedfrom battery through the winding of relay 43, upper back contact ofrelay 88, terminal I3 and one of terminals 4, 5, 3, 1 and 9 of terminalstrip 19, the

segment of commutator 66 with which brush 55 is in engagement, the lowerback contact of relay 83, back contact of release magnet 11, inner lower:back contact of relay 53, to ground at a back contact of relay 43. Ifthe first digit is 2, this (circuit includes the upper back contact ofrelay 88, the outer lower back contact of relay 84, ter- .minals l4 and2 of terminal strip 19, and segment 2 of commutator 65. If the firstdigit is 3, this circuit includes the upper back contact of relay 88,terminal 13 of terminal strip 19, terminal l6 of terminal strip 18,lower back contact of relay 62, terminal l5 of terminal strip 18,terminal 3 of terminal strip 19, and segment 3 of commutator 66. Relay43 locks through its upper front contact, the inner lower back contactof relay 4!], conductor 33, to ground at a front contact of relay 42,this locking circuit being closed before the operating circuit isopened. The operation of relay 43 causes the release of the rotarystepping relay 81, opens the short circuit around resistor 31 so as toprevent further operation of the vertical stepping magnet 15, anddisconnects ground from theconductor leading to the winding of the startrelay 39 of the ringing and tone apparatus RA.

If, on a call to be completed through the main office, all of the trunksto the main office are busy upon seizure of the selector repeater SRI,relay 55 is released due to the operation of relay 51; and, when relay43 operates, busy tone is transmitted to the calling subscriber. To thisend, the upper winding of relay 4'! isconnected through the upper \backcontact of the 11th rotary step springs 68, the lower front contact ofrelay 43, the inner back contact of relay 55, conductor. [09, throughthe winding of relay H2 and the primary winding of the busy transformerBT to ground in the common miscellaneous alarm and register apparatusMA. Relay. H2 operates, closing a circuit for operating relay H3; .andrelay H3 closes a circuit for operating the over-flow register H4. Whenthe calling subscriber releases, relays M, 5, 51, a2 and 43 arereleased. The release of relays 41 and 42' closes a circuit foroperating the release magnet 11, thereby restoring the brushes ofselector BS1 to normal.

If, on a call to be completed through the main ofiice, an idle trunk tothe main ofiice is selected prior to the dialing of the first digit,relay 55 does not release when relay 51 operates, and the brushes ofselector BS! remain opposite the selected level without trunk huntingtherein. The succeeding trains of impulses transmitted over the callingline are repeated over the trunk T' to operate switches in the main andcalled offices to complete the desired connection. The talkingconnection includes back contacts of relay 40, front contacts of relay51, front contacts of relays 51, 45 and 50, and condensers 59wand 60.When the connection is released by the call-v ing subscriber, therelease of relay causes the release of relays 42, 51 and 45; and therelease of relay 42 causes the release of relays 43, 55, 50 and 14, theselector BS! and line finder LF being restored to normal in the mannerabove described.

If the calling subscriber is a restricted service subscriber and thesprings 25 of the line finder LF are actuated, the operation of relayElcloses a circuit for operatively energizing the lower winding of relay38. If then the first digit dialed indicates that a calling subscriberis dated in an office other than the main or the branch ofiice, therelease of relay 58, after relay 41 reoperates at the end of the trainof impulses, closes a circuit for operating relay 89. This circuit istraced from battery through the winding and back contact of relay 8%),outerwpper front contact of relay 88, terminals-of terminal strips 19and '58 as commutator 65 with which brush 65- is-in eng-agement, lowerback contact of relayBfi, upper back contact of release magnet ll, innerlower back contact of relay 53, to ground at a back contact of relay 43.Since relay 88 has been operated, relay G3 is normal. Relay 89 looksthrough its outer lower front contact, back contacts of relays 13 and1-6, conductor 33, to ground at a front contact ofrel-ay 52. Relay 8%]closes a circuit "for operating relay 86 and connects ground through itsupper front contact to test brush 63 to simulate a busy condition on alltest terminals engaged by; this brush. The rotary step-ping magnet it isthereby operated to adabove described, segment of vented. When thecalling subscriber releases the connection, the selector repeater andline finder are restored to normal as above described.

Assume next that the first digit dialed is the digit 8. In this case thecalled line is either in the main or branch office, but it cannot bedefinitely determined whether it is in the one or the other until thesecond digit has been dialed. When relay 53 releases after relay 41operates at the end of the last impulse of the train, itcloses a circuitfor operating relay 84. This circuit is traced from battery through thewinding of relay 84, inner upper back contact of relay 82, terminals l5and 8 of terminal strip 19, terminal 8 of the vertical commutator 65,brush 65, thence to ground at the back contact of relay 43 ashereinbe'fore described. Relay 331010565 a locking. cir-. cuit throughits inner lower front contact, winding of relay.82, through backcontacts of relays 43 and; 4c, conductor 33, to ground at a frontcontact of relay 42'. Relay 82 is, however, shortcircuited through thecommutator brush 65 and does not operate until the operationof releasemagnet 11' opens this short circuit. Relay 84 closes a. circuitforoperating the release magnet 11. This circuit includes the lowerfront contact of springs 67, and the outer upper back contact of relay82. Th v release magnetof theli'ne' finder is not energized at this timebecause'the circuit for operating this magnet is not closed until thecut-through relayv (not shown) of the line finder. is released. Magnet1'! looks through the lower front contact of springs 61, the frontcontact of magnet ll, inner lower back contact of relay 53, to ground ata back contact of relay 43; causes the return of the brushes of selectorSI to normal; and opens the operating circuit of relay 3%. When itsoperating circuit is opened, relay 85 1s held operated in series withthe winding of relay 82, and relay 82 operates in a circuit through backcontactsof relays 43 and 40, com ductor 33, to ground at a front contactof relay 42. When the shaft reaches normal, relay 31 releases, thevertrcaloff-normal springs 61 are restored to normal, and thelowerwinding of relay 85 is operatively energized in series with therelease magnet 77; This circuit includes the middle lower front contactof relay 51, the lower winding and inner lower back contact of.relay.35, the. front contact of magnet ll, thence as above described, toground at a backcontact of relay as. Relay 35 locks through its upperwinding and upper front contact under control of relay 12, the operatingcircuit being opened at its inner lower back contact to release themagnet TI. The aforementioned operation of relay S2 in series with thewindingof relay'fi l disconnects terminal 8 of commutator from thewinding of relay M and connects this terminal to terminal ll. ofterminal strip l9 thence, through terminal E3 of terminal strip 19 andthe upper back Contact of relay 88, to the winding of relay 23. Theimpulses created by the dialing of the second digit cause thereoperaticn of the selector BSE; and .these impulses are repeated overthemain office trunk to operate a sccondselector in the main'ofii'ce. Ifthe second digit is any digit other than 2 or 3, the called line is inthe main ofirce; and the release of relay 53, after the last impulse ofthe train, closes a circuit for operating relay 43; or, if the call isfrom a restricted service subscriber and relay 88 has been operated, therelease of relay 53 closes a circuit for operating relay 89 to effectthe transmission of a busy tone to the calling station. The circuit foroperating relay 43 is traced through the upper back contact of relay 88,terminal I3 of terminal strip 18, through the segment of commutator 56with which the brush 65 is in engagement, lower back contact of relay86, back contact of release magnet 11, through the inner lower backcontact of relay 53, to ground at a back contact of relay 43. Relay 43closes its locking circuit before its operating circuit is opened,inserts resistor 31 in series with the vertical stepping magnet toprevent further operation of this magnet, releases relay 81, anddisconnects ground from the start lead of the ringing and tone apparatusRA. The brushes of the selector remain opposite the selected level andthe succeeding trains of dial impulses received from the calling lineare repeated over the main office trunk to operate selector andconnector switches in the main office to complete the connection to thecalled subscribers line. The talking connection includes condensers 59and 8H and the connection is under the control of the calling station,release being effected as above described.

If the second digit dialed after absorption of a first digit 8 is thedigit 2, the release of relay 53, after the last impulse of the train,closes the above described circuit for operating relay 86; and relay 85causes the advance of the brushes of selector BS! in the second level tohunt for an idle trunk leading to a third selector BS3. When anunguarded set of terminals are engaged by the brushes, relay 49 operatesbut if all tercrninals are guarded, the brushes are advanced to the 11throtary position and a busy tone is transmitted to the calling station.If relay 49 operates, it closes the circuit for operating relays 40 and4|. When relay 40 operates and looks as hereinbefore described, itcauses the release of relays 83, 41, 42, 45, 58 and 55. The release ofrelay 50 opens the bridge across the trunk to the main office to efiectthe release of the switches in the main oilice.

Upon selection of a set of terminals connected to a branch ofiice thirdselector BS3 and operation of relay 48, a circuit is closed foroperating the line relay I1I of selector BS3. This circuit is, tracedfrom battery through the lower winding of relay I1I, inner lower backcontact of relay I14, brush 62, a front contact of relay 48, conductor32, middle brush of line finder LF, conductor I2, through the callingsubscribers station, conductor I I, upper brush of line finder LF,conductor 3i, 2. front contact of relay 48, brush BI, inner upper backcontact of relay I14, upper winding of relay I1I, to ground at a backcontact of the 11th rotary step springs I86. Relay I1I closes a circuitfor operating relay I12; and relay I12 connects ground, throughconductor I18, to the terminal engaged by test brush 63, therebymaintaining a ground potential on conductor 33 to hold relays 48 and 51,to hold the line finder LF, and to hold the line and cut-ofi relay I4.When the calling subscriber dials the third digit of the calledsubscribers number, relay IN is alternately released and reoperated inresponse to each impulse. The release of relay I1I in response to thefirst impulse closes a cir-' lcuit, which includes back contacts ofrelays I14 and IN, the lower front contact of relay I12, the winding ofrelay I13 and the winding of the vertical stepping magnet I11, foroperating relay I13 and magnet I11. The operation of magnet I11 stepsthe brushes up to the first level of the terminal bank. When the shaftmoves out of normal position, the vertical off-normal springs I areactuated, thereby closing a circuit from ground at the upper contact ofrelay I12 through the front contact of relay I13 and upper contact ofsprings I85, for operating relay I15. Relay I15 looks through the backcontact of rotary stepping magnet I18, to ground at the outer upper backcontact of relay I14. When relay I1I releases at the end of the firstimpulse, magnet I11 releases. Relay I13 is slow in releasing and remainsoperated until after relay I1I has reoperated at the end of the lastimpulse of the train. Relay I12 is slow in releasing and remainsoperated during the response of relay I1I to dial impulses. Eachsucceeding release of relay I1I causes the reoperation of steppingmagnet I11, the brushes being thereby raised step by step to the levelcorresponding to the digit dialed. When relay I13 releases after thereoperation of relay I1I at the end of the last impulse of the train, itcloses a circuit including the lower front contact of relay I15 foroperating the rotary step- .ping magnet I18. The operation of magnet I18advances the brushes into engagement with the first set of terminals inthe selected level. Magnet I18 opens the locking circuit of relay I15;and the release of relay I15 opens the operating circuit of magnet I18.If the connected switch connected to the first set of terminals is busy,the test brush I83 encounters ground potential which is extended throughthe lowermost back contact of relay I14, back contact of magnet I18,and. the upper contact of springs I85 to reoperate relay I15. Relay I15again closes the circuit for operating magnet I18, the brushes beingthereby advanced to the next set of terminals. Relay I15 and magnet I 18are in this manner operated and released to advance the brushes until anunguarded set of terminals is encountered; whereupon relay I14 isoperated in a circuit from battery through the winding of relay I15,upper contact of spring I85, back contact of magnet I18, winding ofrelay I14, lower back contact of the 11th rotary step springs I 85, toground at the upper front contact of relay I12. Relay I15 is marginaland does not reoperate in series with relay I14. Relay I14 disconnectsthe windings of relay I1I from the calling line and extends theconnection from the calling line through its front contacts and throughbrushes NH and I82 to the line relay (not shown) of the connector switchBC3 to which the selected set of terminals is connected.

The dialing of the last two digits of the called subscribers numbercontrols the operation of the connector BC3 in usual manner to establishconnection with the called line. If the called line is idle, ringingcurrent is transmitted to signal the called station in usual manner.After relays HI and I 12 of selector BS3 release, the connection ismaintained under the control of the calling subscriber, holding groundpotential in the connector BC3 being connected to the terminal engagedby test brush I83 to hold relay I14 of selector BS3, relays 40 and 51 ofthe selector repeater SRI, to hold the line finder LF,

and to hold the line and cut-off relay [4 in usual manner.

When the connection is released by the calling subscriber, is holdingground potential is disconnected, causing the release of relays I14, 40,51 and I4. The release of relay I14 closes a circuit for operating therelease magnet I19, the brushes of selector BS3 being thereby restoredto normal. The release of relay 4!] closes a circuit including backcontacts of relays 40, 41 and 42 for operating the release magnet 11 ofthe selector BSI and the release magnet 29 of the line finder LF. Thebrushes of the selector and the brushes of the line finder are therebyrestored to normal, the circuits for operating their release magnetsbeing opened at their vertical off-normal springs 61 and 28 when theshafts reach normal. When the called subscriber also releases theconnection, the connector BCS is restored to normal in usual manner.

Assume now that the next digit dialed, after absorption of a first digit8, is the digit 3; in

which case, the brushes of the selector B SI are advanced to the thirdlevel. The release of relay 53 at the end of the last impulse of thetrain, closes a circuit for operating relays 48 and 83 in parallel. Thiscircuit is traced from the winding of relay 48,through terminals l2 andI3 of terminal strip 18, front Contact of relay 84, thence in parallelwith the Winding of relay 83 through terminals II and 14 of terminalstrip 18, the outer lower front contact of relay 82, terminal I5 ofterminal strip 18, terminal 3 of terminal strip 19, segment 3 ofcommutator 6E, brush 65, lower back contact of relay 83, back contact ofrelease magnet 11, inner lower back contact of relay 53, to ground at aback contact of relay 43. The operation of relay 48 causes the releaseof relays 55 and 50, thereby releasing the trunk to the main office andthe operated selector switches therein. A locking circuit for relays 48and 83 is closed through the inner lower front contact of relay 83, theupper front contact of springs 61, back contacts of relays 43 and 40, toground at a front contact of relay 42. Relay 83 closes a circuit foroperating relay 8E. Relay 86 looks under the control of relays 43 and49, and closes a circuit for operating the release magnet 11, thiscircuit being traced from the winding of magnet 11 through the lowerfront contact of springs 61, outer upper front contact of relay 82,inner upper front contact of relay 83, outer upper front contact ofrelay 8%, through back contacts of relays 43 and 4G, to ground at afront contact of relay 42. The operation of magnet 11 restores thebrushes to normal, the return of contact springs 61 to their normalposition being effective to release relays 43 and 83. When the thirddigit of the called subscribers number is dialed, this digit being oneof digits 3 to 9, inclusive, the brushes of the selector BS! arereoperated to select a corresponding level. Relay 81 reoperates as soonas contact 69 closes; and, relay 86 being operated and locked as abovedescribed, the release of relay 53 at the end of the last impulse of thetrain closes the circuit for operating rotary stepping magnet 16,thereby advancing the brushes into engagement with the first set ofterminals inthe selected level. If

the first set of terminals is guarded against seizure, the brushes arefurther advanced until an unguarded set of terminals is encountered;whereupon relays 49, 4| and 4!] are operated as hereinbefore describedto seize the terminals and connect the calling line through brushes 61,I52

and 63 to a connector switch BC2 having access to the called line. Thedialing of the last two digits of the called subscribers number effectsthe operation of the connector switch BCZ to.

'inding of release magnet 11, lower front contact of the verticaloff-normal springs 61, lowermost back contact of relay 85, outer upperback contact of relay 80, terminal I of commutator 66 and brush 65,lower back contact of relay 86, upper back contact of release magnet 11,inner lower back contact of relay 53 to ground at a back contact ofrelay 43. Release magnet 11 looks through the lower front contact of thevertical off-normal springs 61 and upper front contact of magnet 11, toground at the back contact of relay 43. The operation of magnet 11causes the brushes to be restored to normal; and, when the shaft reachesnormal, the opening of the lower contact of springs 61 causes theoperative energization of the lower winding of relay in series with thewinding of the release magnet 11. The circuit for operating relay 85 istraced from battery through the Winding of the release magnet 11, middlelower front contact of relay 51, lower winding and inner lower backcontact of relay 85, front contact of release magnet 11, to ground asabove mentioned at a back contact of relay 43. The operativeenergization of the lower winding of relay 85. effects the closing of alocking circuit through the upper winding and inner upper front contactof relay 85 before the circuit through its lower winding is opened atits inner lower back contact. This locking circuit is traced frombattery through the upper winding and inner upper front contact of relay85, to ground at an upper front contact of relay 42. The opening of thecircuit through the lower winding of relay 85 causes the release ofmagnet 11. The dialing of the second digit l causes the reoperation ofthe selector BSl and the repeating of the impulses over the trunk to themain olfice. The brushes of selector BS4 are stepped up to the firstlevel of the bank vand, when relay 53 releases after the reoperation ofrelay 41, it closes a circuit for operating relay 83. This circuit istraced from battery through the winding of relay 83, terminals H and H]of terminal strip 18, lower front contact of relay 85, outer upper backcontact of relay 80, terminal I of commutator 66 and brush 65, lowerback contact of relay 86, upper back contact of release magnet 11, innerlower back contact of relay 53, to ground at a back contact of relay 43.Relay 83 locks through its inner lower front contact, the upper frontcontact of springs 61, through back contacts of relays 43 and 40,conductor 33, to ground at a front contact of relay 42. Relay 83 closesa circuit for operating relay 86, this circuit including the middleupper front contact of relay 83, and the outer upper back contact ofrelay 86. Relay 8% closes its. locking circuit as hereinbefore tracedbefore its operating circuit is opened, and closes an operating circuitfor the rotary stepping magnet I3. The brushes of selector BSI arethereupon advanced in the first level of the bank until an idle set ofterminals is engaged. If all of the trunks connected to terminals in thefirst level are busy, the brushes are advanced to the llth rotaryposition in which the actuation of springs 68 effects the release ofrelays 5i] and 55 so as to release the trunk to the main office, andeffects the transmission of a busy tone to the calling subscriber byconnecting the upper winding of the line relay 41 to the busy tonetransformer ET in the common miscellaneous alarm and register apparatusMA.

Since the impulses from the digits 11 are repeated over the trunk to themain ofiice, the incoming selector in the main ofiice hunts in the firstlevel of its bank to select a service code selector, and the selectedservice code selector through brush I64 of selector SCS and brush 65' ofselector BSI to cause the operation of relays 40 and M. Relay 56 locksas hereinbefore described, causes the release of relay H, and connectsthe calling line to the trunk OTI. The holding ground potentialconnected to brush I63 holds the selector SCS, holds relays 33 and 51,holds the line finder LF, and holds relay I4. When both the callingsubscriber and called operator release, the selector SCS, selectorrepeater SRI and line finder LF are restored to normal.

hunts in the first level while the selector BSI is hunting for an idleservice code selector in the branch office. If the service code selectorin the main office encounters an all-trunks-busy condition, a busy tonein transmitted from the main office to the calling subscriber in thebranch ofiice, but this does not interfere with the operationof theselected service code selector in the branch oifice; and, if the servicecode selector in the branch office is operated responsive to a thirddigit to complete a connection with a special service trunk ashereinafter described, the trunk to the main oifice is released.

Upon selection of a unguarded set of terminals 'II in level I ofselector BSI, relay 49 is operated as above described. Since relay 83'is operated, the operation of relay 59 closes a-connection from thewinding of relay II, through the upper windingof relay 46, the innerlower front contact of relay I9, and outer upper front contact of relay83, to brush 84 of selector SI, so that operation of relays 4B and IIwill be controlled according to the selection made by the service codeselector SCS in response to the third digit dialed. The service codeselector SCS is similar to the branch office selector BS3. The bank ofselector SCS is represented by two sets of terminals, the upper setrepresenting the tenth level having recording completing trunks to along distance operator connected thereto, and the lower set representinga level which has no trunks connected thereto, selection of this levelindicating that the call is to be completed through the main office.Since relay 43 is not operated, relay 4'!- remains connected to thecalling line and the operation of relay 49 closes a bridge across thebrushes GI and 62 for operating the line relay (not shown) of theservice code selector SCS. This bridge is traced from brush SI, throughthe inner upper front contact of relay 41, and outer upper front contactof relay 69, to brush B2. The impulses created by the dialing of thethird digit are thus repeated by relay 41 to control the group selectingoperation of selector SCS. The brushes of selector SCS are thereuponadvanced in the selected level to hunt for an unguarded set ofterminals.

Assume first that the third digit dialed is the digit 0, in which caseselector 808 trunk hunts in the tenth level and selects an idlerecording completing trunk OTI in this level. The bridge across thebrushes 6| and 62 is thereupon extended through brushes NH and I32 tothe selected trunk circuit which operates in usual manner to connect a.holding ground potential to the terminal engaged by the test brush I63and this ground potential is also connected If the third digit dialed isone which effects the selection of a level having no trunks connectedthereto, the brushes of selector SCS are advanced into engagement withthe first set of terminals in the level and the brush I64 engages aterminal which is connected through a resistor I35 to ground, therebycausing the operation of relay 4!. Relay 40 is marginal and does notoperate. The operation of relay II causes the operation of relay 43.Relay 43 looks under control of relays 4t and 42. The operation of relay43 causes the release of relays 83, i3, 83 and II.

he release of relay 49 opens the bridge across brushes BI and 62 therebycausing the release of the service code selector SCS, the connectionover the trunk to the main office being maintained under the control ofrelays II and 42. When the calling subscribed releases, the selectorrepeater SRI and line finder LF are restored to normal as hereinbeforedescribed.

The selector repeater SRI may be used in a trunking arrangement andnumbering plan such that a group of trunks to another ofiice is connected to one of the levels of selector BSI, or a level of this selectormay represent a route which can be obtained only by calling theoperator. On a call from a restricted service subscribers station, relay83 is operated in the manner above described; and upon selection of thelevel in question, normal post springs III are actuated to cause theadvance of the brushes to the 11th rotary position to actuate springs 68and thereby transmit a busy tone to the calling station.

When the line LI is connected through line finder LP to selectorrepeater SRI as above described, the operation of relay 42 connectsground through its inner lower front contact, upper winding of relay 38,outer upper back contact of relay 51, and lower back contact of relay 88to conductor I03 leading to the timing apparatus TA. If at that timerelay I35 is normal or as soon thereafter as relay I35 releases,conductor I03 is connected to battery and relay 88 operates. Relay 88looks in a circuit from battery through the winding of relay III in themiscellaneous alarm and register apparatus MA, conductor I04, outerlower front contact of relay 88, outer upper back contact of relay 57,upper winding of relay 88, to ground at a front contact of relay 42.Relay III, operated by the current in this circuit, closes circuits foroperating relays II! and I44 and for immediately operating start relayI34 if relay I33 is then normal, or for operating relay I34 as soon asrelay I33 releases. Relay II'I connects ground to conductor I20 tooperate timing relays I2I, I22 and I23. The operation of start relay I34 causes the successive operation of relays I 3|, I32 and I33. Theoperation of relay I3I causes the operation of relay I35, and relay I35disconnects battery from conductor H33- and other like conductors. Theoperation of relay I33, approximately twenty-four seconds after theoperation of relay

